Digital broadcasting has a characteristic that radio disturbance does not easily occur as compared with analog broadcasting. There are several reasons for this. First, in order to make digital broadcasting highly resistant to multipath disturbance, guard intervals are lengthened sufficiently. Second, in order to improve the stability of signals, a double error correction method using an RS code and a convolutional code is used. Third, errors of data are made to be distributed with interleaving in such a manner that an error correction can be effectively made to the errors. Fourth, in order to reduce the reflectivity of electric waves and the energy of pulse noise, a UHF band is used. Thus, in digital broadcasting, although many measures are taken against radio disturbance, in a case of a digital broadcasting receiver mounted in mobile equipment, radio disturbance easily occurs depending on receiving environments as compared with a case of a non-portable digital broadcasting receiver. This radio disturbance causes a block noise which appears on the screen in a case of an image, and causes a sound skip in a case of a sound.
As a measure against such radio disturbance, a method of, in a vehicle-mounted broadcasting receiver, storing the broadcasting signal in a storage medium before the reception has broken off, playing back the broadcast data stored therein when the vehicle enters a region in which no electric wave does not reach, such as a tunnel, and preventing noise from occurring when the reception breaks off is disclosed in patent reference 1. Furthermore, a method of a broadcasting station coding one broadcast program into two types of data: data having a high bit rate and data having a low bit rate, and delivers them through broadcasting or via a communication network, and a receiver playing back a fine image associated with the data having the high bit rate while the reception state is good and playing back an image associated with the data having the low bit rate when the reception state has gotten worse is disclosed by patent reference 2. This reference also shows a technology of using, as a deterioration index of the radio wave state, the radio field intensity or the header information in the broadcast data to solve problems of redundancy of data to be played back and of switching timing. In addition, a method of multiplexing two sets of identical data by shifting them with respect to time, and then broadcasting them, and a receiver playing back the data which are sent thereto later while the reception state is good, and playing back the other data which are sent thereto previously and are held therein when the reception state has gotten worse is disclosed by patent reference 3.    [Patent reference 1] JP, 2001-275049, A (see pp. 2 to 3 and FIGS. 1 and 3)    [Patent reference 2] JP, 2003-134064, A (see pp. 12 and FIGS. 1 and 3)    [Patent reference 3] JP, 2004-320394, A (see pp. 12 and FIGS. 1 and 2)
In the case of the broadcasting receiver described in patent reference 1, a broadcasting signal which is stored in a storage medium and which was received before the reception has broken off is used. However, patent reference 1 does not concretely disclose any information about the data configuration of actual digital broadcasting. A problem is therefore that, for example, because it is not taken into consideration about the storage format of stored data, there is a high possibility that when switching to a playback of stored data at a time when the reception state has gotten worse suddenly, the image and/or the sound break off. Furthermore, in the case of the method disclosed in patent reference 1 or patent reference 2, two data of different formats are generated for an identical broadcast program, and they are transmitted via multiplex broadcasting after a time lag is introduced between them or they are transmitted via different communication networks or the like, respectively, and therefore this method has a problem with infrastructure improvement that the method cannot be implemented unless the broadcasting station side supports this method, and also has a problem that the implementation of the method cannot be carried out only by the receiver.
The present invention is made to solve the above-mentioned problems, and relates to a digital broadcasting receiver which can complete the implementation of a measure against radio disturbance to transmission radio waves of currently available digital broadcasting only by the receiver itself, and which, when switching to stored data during playback of broadcast data, can perform a smooth playback of the stored data by using a devised storage format.